By the end of spring they were fully formed, and many of them having left their shells were to be seen creeping about the earth. I now conjectured that these young worms would be impelled by their instincts to pursue a parasitic existence, and to seek out an animal to inhabit and to grow to maturity in; and it seemed not improbable that the brood I had reared would, like their parents, thrive best in the caterpillar. In order, therefore, to induce my young brood to immigrate, I procured a number of very small caterpillars which the first spring sunshine had just called into life. For the purpose of my experiment I filled a watch-glass with damp earth, taking it from amongst the flower-pots where the threadworms had wintered. Upon this I placed several of the young caterpillars.” The result was as he expected; the caterpillars were soon bored into by the worms, and served them at once as food and home.[30] Frogs and parasites, worms and infusoria--are these worth the attention of a serious man? They have a less imposing appearance than planets and asteroids, I admit, but they are nearer to us, and admit of being more intimately known; and because they are thus accessible, they become more important to us. The life that stirs within us is also the life within them. It is for this reason, as I said at the outset, that although man’s noblest study must always be man, there are other studies less noble, yet not therefore ignoble, which must be pursued, even if only with a view to the perfection of the noblest. Many men, and those not always the ignorant, whose scorn of what they do not understand is always ready, despise the labours which do not obviously and directly tend to moral or political advancement. Others there are, who, fascinated by the grandeur of Astronomy and Geology, or by the immediate practical results of Physics and Chemistry, disregard all microscopic research as little better than dilettante curiosity. But I cannot think any serious study is without its serious value to the human race; and I know that the great problem of Life can never be solved while we are in ignorance of its simpler forms. Nor can anything be more unwise than the attempt to limit the sphere of human inquiry, especially by applying the test of immediate utility. All truths are related; and however remote from our daily needs some particular truth may seem, the time will surely come when its value will be felt. To the majority of our countrymen during the Revolution, when the conduct of James seemed of incalculable importance, there would have seemed something ludicrously absurd in the assertion that the newly-discovered differential calculus was infinitely more important to England and to Europe than the fate of all the dynasties; and few things could have seemed more remote from any useful end than this product of mathematical genius; yet it is now clear to every one that the conduct of James was supremely insignificant in comparison with this discovery.